Typical fracturing completions involve a series of sliding sleeves that provide formation access through a series of dropped balls on seats. The balls start off small to land on the smaller seats further from the well surface and pressure is built up to slide a sleeve so that a port is opened and the zone can be fractured through that port. The process is repeated working toward the well surface and dropping progressively larger balls on progressively larger seats associated with sleeves that open other ports for a continuation of the fracturing process until all the sleeves have been shifted open and fracturing has taken place through each opened sleeve. Each time a larger ball is dropped on a seat the open sleeves below are isolated and fracturing takes place through the single just opened sleeve with a ball in its seat. Some designs of such sleeves allow them to be shifted after fracturing to put a screen at the open port so that production can commence through the screened and open port. A shifting tool can be used after the fracturing is complete to close off the zones that will not be produced. Alternatively the shifting tool can be used to close producing zones if they produce undesirable fluids or sand. Normally production brings the balls up to the surface but this is not always the case as some may get hung up on the seat or seats that are further up.
The following patents relate generally to original fracturing and zone isolation to accomplish fracturing or to removal of barriers used to isolate zone for fracturing: U.S. Pat. Nos. 7,958,940; 6,651,738; 7,591,312; 7,604,055; U.S. Publication 2011/0220362; U.S. Publication 2011/0067870 and 2011/0114319.
The problem that arises if the well has to be re-fractured is that all the sliding sleeve valves with ball seats are still in the wellbore. The sliding sleeve valves could have been open for years and may not close. The presence of the ball seats can also impede progress of other tools to desired locations further down the wellbore. If the well requires refracturing there needs to be a way to isolate individual open ports so that the refracturing can be focused on specific ports for greater effectiveness. Additionally if the preparation of the existing wellbore and the refracturing can occur in a single trip then a greater advantage is achieved in cost savings. The present method allows the refracturing to take place after the bottom hole assembly mills up the ball seats in the existing sliding sleeves. The bottom hole assembly features a packer and a locating collet that allows the tool to enter a sliding sleeve after its seat has been milled out and isolate the open port so that a specific open port is refractured. The process continues up the wellbore until all the desired ports have had the refracturing process take place so that the bottom hole assembly can be removed and the well again put into production. These and other aspects of the present invention will become more readily apparent to a person skilled in the art from a review of the detailed description and associated drawings while recognizing that the full scope of the invention is to be determined by the appended claims.